Among the precise conditions that allow to express a HEFT as a SMEFT, thoroughly studied in [1]}, the first necessary requirement among those spelled out in subsection REF 
is the existence of an \(O(4)\)  symmetric point \(h=h_\ast \) .
This requires a zero, that recalling the Taylor expansion in Eq. (REF ) yields the relation
\(\mathcal {F}(h_\ast )=1+\sum _{n=1}^{\infty }{a_n}\frac{h_\ast ^n}{v^n}=0\;.\) 
